Magnetic tunnel device and magnetic memory using same

ABSTRACT

A magneto-resistance device is composed of an anti-ferromagnetic layer ( 5 ), a pinned ferromagnetic layer ( 20 ), a tunnel insulating layer ( 9 ) and a free ferromagnetic layer ( 21 ). The pinned ferromagnetic layer ( 20 ) is connected to the anti-ferromagnetic layer ( 5 ) and has a fixed spontaneous magnetization. The tunnel insulating layer ( 9 ) is connected to the pinned ferromagnetic layer ( 20 ) and is non-magnetic. The free ferromagnetic layer ( 21 ) is connected to the tunnel insulating layer ( 9 ) and has a reversible free spontaneous magnetization. The pinned ferromagnetic layer ( 20 ) has a first composite magnetic layer ( 6 ) to prevent at lest one component of the anti-ferromagnetic layer ( 5 ) from diffusing into tunnel insulating layer ( 9 ).

TECHNICAL FIELD

The present invention relates to a magnetic tunnel element (amagneto-resistance device) and a manufacturing method of amagneto-resistance device, and more particularly relates to a magnetictunnel element (a magneto-resistance device) including a magnetic tunneljunction (MTJ) to show a tunnel magneto-resistance (TMR) effect, to themanufacturing method of the same, and to a magnetic memory using thesame.

BACKGROUND ART

In recent years, a magnetic head and MRAM (magnetoresistive RandomAccess Memory) using a magneto-resistance element to show GMR (GiantMagneto-Resistance) effect have been developed. The magneto-resistanceelement used in such devices has a structure called spin valve, andincludes an anti-ferromagnetic layer/a ferromagnetic layer/a nonmagneticlayer/a ferromagnetic layer. When the nonmagnetic layer is a conductivelayer formed of material such as Cu, the structure is called aspin-valve type GMR, and when the nonmagnetic layer is an insulatinglayer, the structure is called a spin-valve type TMR (TunnelMagneto-Resistance).

FIG. 1 shows a sectional view of a spin-valve type TMRmagneto-resistance device. With reference to FIG. 1, themagneto-resistance device includes a lower layer 124 as an electrodeformed on a substrate 101; an anti-ferromagnetic layer 123; a pinnedferromagnetic layer 120; a tunnel insulating layer 122; a freeferromagnetic layer 12; and a surface layer 125. The pinnedferromagnetic layer 120 has a spontaneous magnetization whosemagnetization direction is fixed, and the free ferromagnetic layer 121has a spontaneous magnetization whose magnetization direction can beinverted. In order to firmly fix the direction of the spontaneousmagnetization, the pinned ferromagnetic layer 120 is often formed to beconnected to the anti-ferromagnetic layer 123. Consequently, themagnetization is firmly fixed to one direction based on an exchange biasfrom the anti-ferromagnetic layer 123. Exchange interaction that theanti-ferromagnetic layer 123 provides for the pinned ferromagnetic layer120, firmly fixes the spontaneous magnetization of the pinnedferromagnetic layer 120. The anti-ferromagnetic layer 123 is generallyformed of an anti-ferromagnetic material (Mn-based alloy) containing Mn,such as IrMn and PtMn. Also, the free ferromagnetic layer 121 is oftenformed of a hard ferromagnetic layer 121 b formed of a ferromagneticmaterial having a high spin polarization rate, and a soft ferromagneticlayer 121 a formed of a soft ferromagnetic material. Such a structure ofthe free ferromagnetic layer 121 makes it possible to facilitate theinversion of the spontaneous magnetization of the free ferromagneticlayer, while increasing a magneto-resistance change rate (a MR rate) ofthe magnetic tunnel junction. In general, the hard ferromagnetic layer121 b is formed of a ferromagnetic material containing Co, such as Coand CoFe. The soft ferromagnetic layer 121 a is generally formed of aferromagnetic material containing Ni (Ni alloy) such as NiFe, which hassmall magnetization and soft magnetism. The tunnel insulating layer 122as a nonmagnetic layer is formed as a very thin insulating film to anextent that tunnel current can flow through it. The tunnel insulatinglayer 122 is generally formed of an insulator such as AlO_(x). The lowerlayer 124 and the surface layer 125 function as electrodes of themagneto-resistance elements.

In the TMR element, the current flows in the vertical direction to thefilm surface. The magnetization direction of the free ferromagneticlayer is rotated to a magnetic field direction by an external magneticfield, and the resistance of the magneto-resistance element is changeddepending on a relative magnetization angle between the freeferromagnetic layer and the pinned ferromagnetic layer.

One of the problems in using the TMR element as an MRAM element is athermal stability. It is necessary for manufacture of the MRAM to use aprocess of manufacturing a semiconductor device. For example, in aprocess of forming a wiring line and an insulating film, and in athermal treatment process in hydrogen atmosphere for improving theperformance of a transistor, it is assumed that the temperature ofnearly 400° C. is applied to the TMR element. The conventional TMRelement has a low heat resistant temperature of 300° C. Therefore, ifthese processes are applied as they are to the MRAM including the TMRelements, an elements characteristic is deteriorated. One of the reasonsof the deterioration is diffusion between layers of themagneto-resistance elements when the high temperature is applied to themagneto-resistance elements.

As described above, when the conventional TMR element is used as theMRAM element, it is always necessary to consider the thermal treatmenttemperature in the manufacturing process. Therefore, available devicestructures and manufacturing processes are limited. In this way, it isdemanded to improve a thermal resistance of the TMR element in order toachieve a high-performance MRAM with excellent reliability and to reducea manufacturing cost. The thermal resistance of up to approximately 400°C. is desired.

For example, in Japanese Laid Open Patent Application (JP-P2000-20922A:a first conventional example), the diffusion between the softferromagnetic layer and the hard ferromagnetic layer in a free layer isdescribed. A problem pointed out here is the diffusion of Ni containedin the soft ferromagnetic layer into the hard ferromagnetic layer. Thediffusion of Ni into the hard ferromagnetic layer deteriorates thecharacteristic of the magneto-resistance element. In the firstconventional example, an oxide film or a nitride film formed ofnonmagnetic elements is provided between the hard ferromagnetic layerand the soft ferromagnetic layer to prevent the interdiffusion.

However, when the hard ferromagnetic layer and the soft ferromagneticlayer are separated by such an oxide film and the like, the magneticcoupling is extremely weakened sometimes since direct exchangeinteraction between the above two layers is lost. Coercive force of thefree ferromagnetic layer becomes large even if the diffusion preventinglayer is thinned exceedingly. As a result, steepness in magnetizationinversion might be lost.

In Applied Physics Letters (Vol. 78, May 7, 2001, pp. 2911-2913) (thesecond conventional example), Zongzhi Zhang, et al., report a TMRelement that shows a high MR ratio even after a thermal treatment at ahigh temperature, by forming an oxide layer of ferromagnetic elementssuch as FeO_(x), CoFeO_(x), and the like, between the pinnedferromagnetic layer and the tunnel insulating layer. In this method,however, the oxide layer of the ferromagnetic elements decreases the MRratio and increases the junction resistance. This is because the oxideof the ferromagnetic element, e.g., CoO_(x), is an anti-ferromagneticinsulator, which functions as a tunnel barrier of undesirable propertythat causes a leakage current not depending on a spin, and a spinscattering of tunneling electrons. In addition, CoO_(x), FeO_(x), andNiO_(x), as the oxides of Co, Fe, and Ni have high oxide generation freeenergy and are instable, and are decomposed in a temperature range of300° C. to 350° C. Therefore, it is difficult to obtain a thermalresistance of near to 400° C.

In Japanese Laid Open Patent Application (JP-P2001-237471A) (a thirdconventional example), an oxide magnetic layer is inserted in the pinnedferromagnetic layer and the free ferromagnetic layer in a spin valvetype GMR element, in order to improve thermal stability of exchangecoupling of the pinned ferromagnetic layer, and to increase the MR ratiothrough increase in resistance of the magnetic layer. An oxide magneticlayer is used such as Fe₃O₄ and CoFe₂O₄ containing iron oxide as a maincomponent and they are added with Si, Al, B, N, Y, and La. In such aspin valve type GMR element that electric current flows in a plane, thehigh resistance of the pinned ferromagnetic layer prevents thedistribution of the electric current out of the conductive layer in thespin valve type GMR element other than the nonmagnetic layer, and the MRratio can be increased. However, in the TMR element in which theelectric current flows in the direction perpendicular to the plane and amagnetoresistance effect of the tunneling current is important, theabove-mentioned effect of increasing the MR ratio cannot be expected.Oppositely, in the oxide magnetic layer functions as a series resistancethat does not contribute to the tunneling magneto-resistance in the TMRelement. Therefore, all the element resistances increase, so that S/N(signal-to-noise) ratio is decreased.

In Japanese Laid Open Patent Application (JP-P2002-158381A) (a forthconventional example), a problem is pointed out that Mn diffuses fromthe anti-ferromagnetic material containing Mn into the pinnedferromagnetic layer. In the fourth conventional example, the pinnedferromagnetic layer is formed from two ferromagnetic layers and aninsulating layer or an amorphous magnetic layer (a diffusion preventinglayer) that is provided between the above-mentioned ferromagneticlayers. Thus, Mn is prevented from diffusing into the pinnedferromagnetic layer.

However, in such a diffusion prevention layer, the metal ferromagneticlayer is separated by the diffusion preventing layer, which causes thefollowing problems. When the insulating layer formed of oxide is used asthe diffusion preventing layer, the resistance of the diffusionpreventing layer is also added in series to the tunnelingmagneto-resistance, and functions as an additional resistance. In thiscase, the S/N (signal-to-noise) ratio of the output of the TMR elementdecreases. In addition, when the insulating layer of the oxide of thenon-magnetic element is used as the diffusion preventing layer, themagnetic coupling between the two separated ferromagnetic layers isexceedingly weakens even if the diffusion preventing layer becomesthinner. As a result, the magnetization of the pinned ferromagneticlayer is not fixed to one direction. Even in case that the diffusionpreventing layer is the insulating layer that contains the oxide of theferromagnetic element, only Fe_(3-X)O₄ (0<x<⅓) indicates theferromagnetism, which includes (CoFe₂) O₄ (Co ferrite), Fe₃O₄(magnetait), and γ-Fe₂O₃ (maghematait) having a spinel structure. Theother oxides of ferromagnetic elements are an anti-ferromagneticmaterial or a paramagnetic material. Moreover, even if the diffusionpreventing layer is formed of a spinel oxide ferromagnetic substance,there is a problem of the thermal instability that oxygen decoupleseasily at a high temperature as mentioned above.

Further, the amorphous magnetic layer is in a non-equilibrium state andtends to be changed generally into a more stable state (e.g., throughcrystallization, including a material of peripheral film) in applicationof heat. The tendency greatly depends on the material. Therefore, itcannot be always said that the amorphous magnetic layer itself iseffective for the diffusion prevention.

As mentioned in the first to fourth conventional examples, in themagneto-resistance element, in which the oxide layer of the non-magneticelement or the oxide layer of the ferromagnetic element is inserted,there are the problems such as the deterioration of MR characteristic,the low thermal stability, the increase of the resistance through theinsertion of the oxide layer, the decrease of the S/N (signal-to-noise)ratio due to the increase of the resistance, and the remarkable decreaseof the ferromagnetic coupling between the two ferromagnetic layersseparated by the oxide layer. Therefore, it has been necessary toprevent the diffusion and solve these problems at the same.

As the result of examining the thermal deterioration mechanism of the MRelement in the thermal treatment at approximately 400° C., the inventorsof the present invention found that Ni in the free ferromagnetic layerdiffuses into the tunnel insulating layer (tunnel barrier) at the hightemperature, and the diffusion of Mn in the anti-ferromagnetic layerinto the tunnel insulating layer especially cause of the thermaldeterioration. Since Ni and Mn diffuse at a relatively low temperature,the deterioration of the tunnel insulating layer due to the diffusion ofNi and Mn is serious.

Therefore, a technique is demanded that diffusion of Ni in the freeferromagnetic layer into the tunnel insulating layer (tunnel barrier) atthe high temperature can be prevented without losing the characteristicof the TMR element in a stable state. Further, a technique is demandedthat the diffusion of Mn in the anti-ferromagnetic layer into the tunnelinsulating layer can be prevented.

In conjunction with the above-mentioned description, a thin filmmagnetic head is disclosed in Japanese Laid Open Patent Application(JP-A-Showa 62-132211). In this conventional thin film magnetic head,the change in an applied signal magnetic field is detected as a changein the resistance of a ferromagnetic thin film having one-axis magneticanisotropy. The thin film magnetic head has the ferromagnetic thin filmformed between SiO₂ films.

Also, a composite bias magneto-resistance effect head is disclosed inJapanese Laid Open Patent Application (JP-A-Heisei 3-268216). In thisconventional technique, the composite bias magneto-resistance effecthead has a three-layer film of a permalloy thin film as amagneto-resistance effect film formed on substrate, a Nb thin film forshunt bias, and a soft magnetic bias film. A magneto-striction of thepermalloy thin film is from +2×10⁻⁶ to −2×10⁻⁶.

Also, a magneto-resistance element is disclosed in Japanese Laid OpenPatent Application (JP-P2002-190631A). In this conventional technique,the magneto-resistance element includes a middle layer and a pair ofmagnetic layers putting the middle layer therebetween. One of themagnetic layers is a pinned magnetic layer, which is hard to bemagnetically inverted against external magnetic field, compared with theother magnetic layer. The pinned magnetic layer is a multi-layered filmof at least one non-magnetic layer and magnetic layers putting thenon-magnetic substance layer therebetween. The magnetic layers aremagnetostatically or anti-ferromagnetically coupled through thenon-magnetic substance layer. When the mth magnetic layer (m is aninteger more than 0) from a middle layer side is referred to as amagnetic layer m, and the average saturation magnetization and theaverage film thickness of the magnetic layer m are assumed to be Mm anddm, respectively, 0.5<Mde/Mdo<1 is met, if a total summation of Mm*dm incase that m is an odd number is Mdo, and the total summation of Mm*dm incase that m is an even number is Mde.

DISCLOSURE OF INVENTION

Therefore, an object of the present invention is to provide amagneto-resistance device that thermal stability (thermal treatmentresistance) is improved, a manufacturing method of the same, and amagnetic memory using the same.

Another object of the present invention is to provide amagneto-resistance device that while magnetic coupling and electricalcontact are kept in each of a pinned ferromagnetic layer and a freeferromagnetic layer, diffusion of elements contained the layer,especially, Ni and Mn into a tunnel insulating layer can be prevented, amanufacturing method of the same, and a magnetic memory using the same.

Still another object of the present invention is to provide amagneto-resistance device that high performance and high reliability canbe accomplished, a manufacturing method of the same that a manufacturingcost can be reduced, and a magnetic memory using the same.

In an aspect of the present invention, a magneto-resistance device iscomposed of an anti-ferromagnetic layer, a pinned ferromagnetic layer, atunnel insulating layer and a free ferromagnetic layer. The pinnedferromagnetic layer is connected to the anti-ferromagnetic layer and hasa fixed spontaneous magnetization. The tunnel insulating layer isconnected to the pinned ferromagnetic layer and is non-magnetic. Thefree ferromagnetic layer is connected to the tunnel insulating layer andhas a reversible free spontaneous magnetization. The pinnedferromagnetic layer is composed of a first composite magnetic layerfunctioning to prevent at least one component of the anti-ferromagneticlayer from diffusing into the tunnel insulating layer. In theabove-mentioned magneto-resistance device, the anti-ferromagnetic layercontains Mn and the first composite magnetic layer has a function toprevent Mn from diffusing into the tunnel insulating film.

In the above-mentioned magneto-resistance device, the first compositemagnetic layer is composed of ferromagnetic material which has been notoxidized and oxide of a material which is easy to bind with oxygencompared with the ferromagnetic material. In the above-mentionedmagneto-resistance device, the ferromagnetic material contains Co as amain component.

In the above-mentioned magneto-resistance device, the first compositemagnetic layer may be formed from an amorphous phase as whole and may beformed from the amorphous phase and a crystalline phase. The crystallinephase contains a plurality of crystalline regions and the plurality ofcrystalline regions pass through the first composite magnetic layer intoa direction of the thickness of the first composite magnetic layer.

In the above-mentioned magneto-resistance device, the compositionformula of the amorphous phase in the first composite magnetic layer isD_(z)M_(1-z)O_(x) (0.6≦Z≦0.9, and X>0). Here, D is at least one selectedfrom the group consisting of Co, Fe and Ni, and M is at least oneselected from the group consisting of Ta, Zr, Hf, Nb, and Ce.

In the above-mentioned magneto-resistance device, the first compositemagnetic layer contains a plurality of crystal grains formed of theferromagnetic material and the plurality of crystal grains are separatedfrom each other by the oxide. Also, a part of the plurality of crystalgrains may be contact with another of the plurality of crystal grains.

In the above-mentioned magneto-resistance device, the oxide containsoxide of at least one element selected from the group consisting of Al,Si, the Mg and Ti.

In the above-mentioned magneto-resistance device, the first compositemagnetic layer contains a plurality of crystal grains formed of theferromagnetic material and the plurality of crystal grains are separatedfrom each other by the oxide. Also, the plurality of crystal grains passthrough the first composite magnetic layer into a direction of thethickness of the first composite magnetic layer. A part of the pluralityof crystal grains may contact with another of the plurality of crystalgrains. The oxide contains oxide of at least one element selected fromthe group consisting of Al, Si, the Mg, Ti, Ta, Hf, Zr, Nb and Ce.

In the above-mentioned magneto-resistance device, it is preferable thatthe thickness of the oxide is thinner than the grain diameter of each ofthe plurality of crystal grains, and it is preferable that the thicknessof the oxide is equal to or less than 2 nm.

In the above-mentioned magneto-resistance device, the average graindiameter of the plurality of crystal grains is preferably equal to orless than 10 nm and the plurality of crystal grains are preferablyferromagnetically coupled.

In the above-mentioned magneto-resistance device, the pinnedferromagnetic layer contains a first metal ferromagnetic layer and asecond metal ferromagnetic layer and the first composite magnetic layeris interposed between the first metal ferromagnetic layer and the secondmetal ferromagnetic layer. It is preferable that the resistivity of thefirst composite magnetic layer is in a range between 10 μΩcm and 3000μΩcm.

In the above-mentioned magneto-resistance device, the free ferromagneticlayer is composed of a second composite magnetic layer functioning toprevent at least one component of the free ferromagnetic layer fromdiffusing into the tunnel insulating layer. The free ferromagnetic layercontains Ni and the second composite magnetic layer prevents Ni fromdiffusing into the tunnel insulating film.

In the above-mentioned magneto-resistance device, the free ferromagneticlayer is composed of a metal ferromagnetic layer and a soft magneticlayer. Here, the metal ferromagnetic layer is connected to the tunnelinsulating layer on one side of the phase boundaries and is connected tothe second composite magnetic layer on the other phase boundary side.The soft magnetic layer contains Ni and is joined to the phase boundaryof the second composite magnetic layer opposite to the metalferromagnetic layer.

In the above-mentioned magneto-resistance device, the pinnedferromagnetic layer is composed of a non-magnetic layer and twoferromagnetic layers anti-ferromagnetically through the non-magneticlayer, and the free ferromagnetic layer is composed of a non-magneticlayer and two ferromagnetic layers anti-ferromagnetically coupledthrough the non-magnetic layer.

In order to solve the above problems, I a method of manufacturing methodof a magneto-resistance device of the present invention, ananti-ferromagnetic layer containing Mn is formed above a substrate and apinned ferromagnetic layer with a fixed spontaneous magnetization isformed on the anti-ferromagnetic layer. Here, the pinned ferromagneticlayer is composed of a first composite magnetic layer functioning toprevent Mn from diffusing into the tunnel insulating layer. Aninsulative non-magnetic tunnel insulating layer is formed on the pinnedferromagnetic layer, and the free ferromagnetic layer with a reversiblefree spontaneous magnetization is formed on the tunnel insulating layer.The first composite magnetic layer is formed of ferromagnetic materialwhich is not oxidized as a main component, and oxide of material that iseasy to bind with oxygen compared with the ferromagnetic material, as asub component.

In the formation of the pinned ferromagnetic layer in theabove-mentioned method of manufacturing the magneto-resistance device,the first composite magnetic layer is formed by the reactive sputteringmethod in a mixture atmosphere of an inactive gas and an oxygen gas, byusing a target which contains at least one of ferromagnetic materialselected from the group consisting of Co, Ni and Fe and at least one ofnon-magnetic material selected from the group consisting of Al, Si, theMg, Ti, Ta, Hf, Zr, Nb and Ce. At this time, in the reactive sputteringmethod, it is preferable that a ratio of a flow rate of the oxygen to aflow rate of the inactive gas is equal to or less than 0.2.

In order to improve the thermal resistance of a TMR device as themagneto-resistance device, a structure is effective in which a diffusionpreventing layer is provided between a layer containing elements such asMn and Ni easy to be diffused and a tunnel insulating layer, and such amaterial is not contained between the diffusion preventing layer and thetunnel insulating layer. In the present invention, an oxide layercontained in the diffusion preventing layer is effective to thediffusion prevention. The oxide has a high thermal reliability, a highdensity, and a large generation energy of the lattice defect, comparedwith non-oxide layer. Therefore, the diffusion coefficient of themagnetic atom to the oxide layer is small. In addition, Mn has aproperty to easily bind with oxygen, and stably bind with oxygen in anoxide and is captured in the oxide. Therefore, it is effective toprevention of Mn diffusion.

The ferromagnetic material in the composite magnetic layer as thediffusion preventing layer is almost in a metal state, and a strongmagnetic coupling can be kept between the layers on the up and downsides connected with the composite magnetic layer by this metalferromagnetic material and moreover the conductive state can be alsokept. In this way, Mn is captured by the non-magnetic oxide (the oxidelayer) which is contained in the composite magnetic layer and thediffusion of Mn is prevented. Here, it is preferable that the materialof the non-magnetic oxide is easy to bind with oxygen, compared with theferromagnetic material. This is to prevent that the ferromagneticmaterial is oxidized, through binding of oxygen with the material. Also,it is preferable that the non-magnetic oxide is stable at 400° C. Thisis to get the effect of the Mn capture at 400° C. As such a material, itis preferable to use a non-magnetic material of Hf, Zr, Nb, Ce, Al, Si,Mg, and Ti which are easy to bind with oxygen compared with theferromagnetic material of Co, Fe and Ni and whose oxide is stable at400° C. These non-magnetic materials have low oxide formation energiescompared with the ferromagnetic material, and are easy to bind withoxygen.

It should be noted that the structure of the magneto-resistance deviceand the manufacturing method of it in the present invention is notlimited to the TMR device. When a non-magnetic conductive layer is usedin place to the tunnel insulating layer and the present invention isapplied to the GMR device, the thermal resistance of a spin valve GMRdevice can be improved through the prevention effect of diffusion of Mnand Ni into the non-magnetic conductive layer in addition to the above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing a structure of a conventionalmagneto-resistance device;

FIG. 2 is a sectional view showing a structure of a magneto-resistancedevice according to a first embodiment of the present invention;

FIG. 3 is a sectional view showing the structure of themagneto-resistance device according to a second embodiment of thepresent invention;

FIG. 4 is a sectional view showing a first example of a compositemagnetic layer;

FIG. 5 is a sectional view showing a second example of the compositemagnetic layer;

FIG. 6 is a sectional view showing a third example of the compositemagnetic layer;

FIG. 7 is a graph showing resistivity of a thin film;

FIG. 8 is a graph showing saturation magnetization of the film shownwith FIG. 7;

FIG. 9 is data showing Co_(2p) spectra of films by XPS;

FIG. 10 is graphs showing relation of thermal treatment temperature anda diffusion quantity of Mn;

FIG. 11 is graphs showing magnetization curves of anti-ferromagneticlayer/pinned ferromagnetic layer—exchange coupling films;

FIG. 12 is a sectional view showing the structure of themagneto-resistance device according to a third embodiment of the presentinvention;

FIG. 13 is a sectional view showing the structure of themagneto-resistance device according to a fourth embodiment of thepresent invention;

FIG. 14 is a sectional view showing the structure of themagneto-resistance device according to a fifth embodiment of the presentinvention;

FIG. 15 is graphs showing relation of thermal treatment temperature andMR ratios in the magneto-resistance devices;

FIG. 16 is graphs showing magneto-resistance curves after thermaltreatment of the magneto-resistance devices;

FIG. 17 is a table showing a relation of MR ratio and exchange couplingmagnetic field in the magneto-resistance devices; and

FIG. 18 is graphs showing the magnetization curve of each sample.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a magneto-resistance device of the present invention willbe described with reference to the attached drawings.

First, a configuration of the magneto-resistance device according to thefirst embodiment of the present invention will be described. FIG. 2 is across-sectional view showing a configuration of the magneto-resistancedevice according to the first embodiment of the present invention.Referring to FIG. 2, the magneto-resistance device in the firstembodiment includes a magneto-resistance element 23. A lower layer 24 isformed on a substrate 1 as a wiring layer. The magneto-resistanceelement 23 is formed on the lower layer 24. A surface layer 25 is formedon the magneto-resistance element 23. The magneto-resistance device inthe first embodiment is applicable to a memory cell of MRAM of across-point cell type.

The lower layer 24 includes a lower electrode seed layer 2, a lowerelectrode layer 3, and a buffer layer 4, which are formed on thesubstrate 1 in this order. The lower layer 24 connects themagneto-resistance element 23 with the lower electrode layer 3electrically. The lower electrode seed layer 2 controls the orientationsof the lower electrode layer 3 and the buffer layer 4. The lowerelectrode seed layer 2 is typically formed of Ta and Cr. The lowerelectrode layer 3 is a wiring layer for the magneto-resistance element23. The lower electrode layer 3 is typically formed of Al₉₀Cu₁₀. Thebuffer layer 4 controls the orientation of an anti-ferromagnetic layer 5provided on the buffer layer 4 to stabilize the anti-ferromagnetic phaseof the anti-ferromagnetic layer 5. The buffer layer 4 is typicallyformed of NiFe and CoFe.

The surface layer 25 includes an electrode contact layer 11 and an upperelectrode layer 12, which are formed sequentially on themagneto-resistance element 23. The surface layer 25 contacts themagneto-resistance element 23 with the upper electrode layer 12electrically. The electrode contact layer 11 is typically formed of TiN,Ta, Ru, W, Zr, and Mo. The upper electrode layer 12 is a wiring layerfor the magneto-resistance element 23. The upper electrode layer 12 istypically formed of Al₉₀Cu₁₀.

The magneto-resistance element 23, functioning as a memory cell of theMRAM, includes the anti-ferromagnetic layer 5, a pinned ferromagneticlayer 20, a tunnel insulating layer 9, and a free ferromagnetic layer21. A magnetic tunnel junction is configured of the pinned ferromagneticlayer 20, the tunnel insulating layer 9, and the free ferromagneticlayer 21. The anti-ferromagnetic layer 5 is provided on the lower layer24, and formed of an anti-ferromagnetic material containing Mn (Mn-basedalloy), and typically, formed of PtMn and IrMn. The anti-ferromagneticlayer 5 imposes an exchange interaction to the pinned ferromagneticlayers 20 that are formed directly on the anti-ferromagnetic layer 5, tofix the direction of a spontaneous magnetization of the pinnedferromagnetic layer 20.

The pinned ferromagnetic layer 20 is provided on the anti-ferromagneticlayer 5, and has a fixed spontaneous magnetization. More specifically,the pinned ferromagnetic layer 20 includes a composite magnetic layer 6and a metal ferromagnetic layer 7 formed on the anti-ferromagnetic layer5 in this order. The metal ferromagnetic layer 7 is formed of a metalferromagnetic alloy with a high spin polarization rate, and typically,formed of CoFe. CoFe alloy is a ferromagnetic substance that isrelatively hard magnetic (that is, coercive force is large). Asdescribed later, the spontaneous magnetization of the pinnedferromagnetic layer 20 is fixed by the exchange interaction from theanti-ferromagnetic layer 5. The composite magnetic layer 6 has afunction to prevent at least one of elements forming theanti-ferromagnetic layer 5 (for example, Mn) from diffusing into thetunnel insulating layer 9. The composite magnetic layer 6 is formed of aferromagnetic material which has been not oxidized and an oxide of thematerial that is easy to bind with oxygen compared with theferromagnetic material. The details are described later.

The tunnel insulating layer 9 is provided on the pinned ferromagneticlayer 20, and is formed of a non-magnetic insulator thin to an extentthat a tunneling current flows. The tunnel insulating layer 9 istypically formed of AlOx, AlNx, and MgOx. The thickness is set inaccordance with a resistance requested to the magneto-resistance element23, and is typically 1.2 to 2 nm. The resistance of the tunnelinsulating layer 9 in the direction of the thickness is different inaccordance with whether the spontaneous magnetizations of the pinnedferromagnetic layer 20 and the free ferromagnetic layer 21 are parallelor anti-parallel, because of an effect of tunneling magneto-resistance(TMR effect). The data stored in the magneto-resistance element 23 canbe determined based on the resistance value in the direction of thethickness of the tunnel insulating layer 9.

The free ferromagnetic layer 21 is provided on the tunnel insulatinglayer 9, and the direction of the spontaneous magnetization isinvertible. Moreover, the free ferromagnetic layer 21 is formed so thatthe direction of the spontaneous magnetization directs in parallel oranti-parallel to the spontaneous magnetization of the pinnedferromagnetic layer 20. The magneto-resistance element 23 stores a dataof one bit as the direction of the spontaneous magnetization of the freeferromagnetic layer 21. The free ferromagnetic layer 21 includes a metalferromagnetic layer 8 and a soft magnetic layer 10. The metalferromagnetic layer 8 is formed of a metal ferromagnetic alloy with ahigh spin polarization rate, and typically formed of ferromagneticsubstance containing Co such as Co and CoFe. The CoFe alloy isrelatively hard magnetic ferromagnetic substance. The soft magneticlayer 10 is formed of a ferromagnetic substance containing Ni, andtypically formed of a ferromagnetic substance (Ni alloy) containing Nisuch as NiFe that is a soft magnetic material and has a smallmagnetization. In general, the ferromagnetic substance containing Ni isrelatively soft magnetic (that is, coercive force is small). Such astructure of the free ferromagnetic layer 21 makes the reverse of thespontaneous magnetization in the free ferromagnetic layer facilitatewhile increasing the magneto-resistance change ratio (MR ratio) in themagnetic tunnel junction.

Next, the composite magnetic layer 6 will be further described. Asdescribed above, the diffusion of Mn contained in the anti-ferromagneticlayer 5 into the tunnel insulating layer 9 is not preferable because theMR ratio of the magnetic tunnel junction is deteriorated. In order toprevent Mn contained in the anti-ferromagnetic layer 5 from diffusinginto the tunnel insulating layer 9, the pinned ferromagnetic layer 20 ispreferably formed from the composite magnetic layer 6 and the metalferromagnetic layer 7 as shown in FIG. 21.

The composite magnetic layer 6 is formed on the anti-ferromagnetic layer5, and prevents Mn of the anti-ferromagnetic layer 5 from diffusing intothe tunnel insulating layer 9 as described later. The metalferromagnetic layer 7 is provided on the composite magnetic layer 6. Atthis time, the metal ferromagnetic layer 7 has a high spin polarizationrate, and is preferably formed of the metal ferromagnetic alloyincluding Co as a main component, which has thermal stability and ishard to diffuse easily. The metal ferromagnetic layer 7 becomes hard inmagnetism by forming the metal ferromagnetic layer 7 of the metalferromagnetic alloy including Co as the main component. Moreover,because the metal ferromagnetic layer 7 has no Ni (or a little), thereis no possibility for Ni to be diffused. Here, the phrase “including Coas the main component” means that it is Co that the atomic percent isthe highest in elements of the metal ferromagnetic alloy.

This structure has advantages that it is possible to reduce the filmthickness of the pinned ferromagnetic layer 20 and reduce the number oflayers of the magneto-resistance element. Moreover, the high MR ratiocan be attained by using the metal ferromagnetic layer 7 for aninterface with the tunnel insulating layer 9 (a tunnel barrier layer).

FIG. 3 is a cross-section view showing a configuration of themagneto-resistance device according to the second embodiment of thepresent invention. In the second embodiment, the pinned ferromagneticlayer 20 has a configuration in which the composite magnetic layer 6 isinserted in the metal ferromagnetic layer 7. That is to say, the pinnedferromagnetic layer 20 has a three-layered structure in which thecomposite magnetic layer 6 is sandwiched by a metal ferromagnetic layer7 a and a metal ferromagnetic layer 7 b. In this case, the same effectas the above-mentioned effect can be achieved.

The composite magnetic layer 6 has electrical conductivity like metal.It is desirable that the resistivity is small to an extent that it canbe completely negligible compared with the tunneling magneto-resistanceeven if the thickness of the composite magnetic layer 6 is thickened toa considerable extent. The value of resistivity is preferably in a rangefrom 10 μΩcm to 3000 μΩcm.

The composite magnetic layer 6 is a composite thin film, which containsmetal ferromagnetic substance, which has been not oxidized, as a maincomponent, and oxide of non-magnetic element, easy to bind with oxygencompared with the above-mentioned metal ferromagnetic substance, as asub component. The composite magnetic layer 6 can prevent Mn fromdiffusing while maintaining the electrical conductivity like metal andferromagnetism. CoFe is typically exemplified as the metal ferromagneticsubstance of the composite magnetic layer 6. As oxides, TaO_(x),HfO_(x), NbO_(x), ZrO_(x), CeO_(x), AlO_(x), MgO_(x), SiO_(x), andTiO_(x) are exemplified. These non-magnetic elements have a lower oxidegeneration free energy and are easy to be oxidized, compared with theferromagnetic elements Fe, Co, and Ni. As a ferromagnetic materials usedfor the composite magnetic layer 6, it is preferable to use Co or themetal ferromagnetic alloy containing Co as the main component. Co or themetal ferromagnetic alloy containing Co as the main component have ahigh spin polarization rate, and are hard to be oxidized. Also, they arehard to be diffused due to thermal stability.

It is important for the composite magnetic layer 6 to contain the metalferromagnetic substance, which has been not oxidized, as the maincomponent in that the composite magnetic layer 6 shows the electricalconductivity and the ferromagnetism. A S/N (Signal-to-Noise) ratio isimproved in a reading operation since the composite magnetic layer 6 hasa metal electrical conductivity. An exchange interaction of theanti-ferromagnetic layer 5 can act to the metal ferromagnetic layer 7due to the composite magnetic layer 6 having the ferromagnetism, so thatboth of the composite magnetic layer 6 and the metal ferromagnetic layer7 are made possible to function as the pinned ferromagnetic layer 20. Toprevent the metal ferromagnetic substance of the composite magneticlayer 6 from being oxidized, the oxide of non-magnetic element is used,which is easily oxidized compared with the metal ferromagneticsubstance, as the oxide of the composite magnetic layer 6.

The composite magnetic layer 6 has any of structures shown in FIG. 4 toFIG. 6 in accordance with component materials and a manufacturingmethod, e.g., the composition ratio of non-magnetic element and themetal ferromagnetic element, and the atomic radius of the non-magneticelement of the oxide. FIG. 4 is a cross section view of the compositemagnetic layer 6 in a first example. When the oxide of the materialhaving a larger atomic radius than that of the metal ferromagneticsubstance is contained in the metal ferromagnetic substance in a highdensity, the structure of the composite magnetic layer 6 has a structurein which the whole of structure is configured of an amorphous phase or astructure is configured of the amorphous phase and a pillar-shapedcrystalline phase (crystalline area). FIG. 4 shows the structurecontaining an amorphous phase 32 and a pillar-shaped crystalline phase33. The reason why the composite magnetic layer 6 takes such a structureis that the crystallization of the metal ferromagnetic substance isobstructed by the non-magnetic element with a large atomic radius.

The pillar-shaped crystalline phase 33 exists as a plurality ofpillar-shaped crystalline areas in the amorphous phase 32 or anamorphous film. The pillar-shaped crystalline phase 33 passes throughthe composite magnetic layer 6 in the direction of the thickness. Thepillar-shaped crystalline phases 33 are mutually separated by theamorphous phase 32. A ferromagnetic metal cluster occupies in a majorportion of the amorphous phase 32, and a non-magnetic oxide cluster iscontained at random in some portions. Mn is captured by the non-magneticoxide cluster, which exists at random in the composite magnetic layer 6,and the magnetic coupling and the electrical conductivity are secured bythe ferromagnetic metal occupying in the major portion of the compositemagnetic layer 6.

A composition of the amorphous phase 32 in the composite magnetic layer6 has a composition formula of D_(z)M_(1-Z)O_(X). Here, “D” is at leastone of Co, Fe, and Ni. M is at least one of Ta, Hf, Zr, Nb, and Ce. Zsatisfies the rage of 0.6≦Z≦0.9 (X>0) as the composition ratio. Also,segregation of the ferromagnetic metal occurs in a region of thepillar-shaped crystalline phase 33, and this region contributes toimprove the magnetic coupling and the electric coupling with upper andlower layers. For instance, when CoFe is used as the metal ferromagneticsubstance, and any of TaO_(x), HfO_(x), ZrO_(x), NbO_(x), and CeO_(x) isused as the oxide of the composite magnetic layer 6, the compositemagnetic layer 6 has the structure as shown in FIG. 4.

FIG. 5 is a cross sectional view of the composite magnetic layer 6 in asecond example. If the atomic radius of the non-magnetic element of theoxide is smaller than that of the element of the metal ferromagneticsubstance, the composite magnetic layer 6 has a structure that there area plurality of ferromagnetic metal crystal grains 35 as grainy crystalsof the metal ferromagnetic substance, and non-magnetic oxides 34precipitated in the grain boundaries of the ferromagnetic metal crystalgrains 35. The material having such a structure is sometimes called as agranular alloy. In this case, some crystal grain of the plurality offerromagnetic metal crystal grains 35 is not completely isolated, and iscontact with adjacent one or more crystal grains of the other theferromagnetic metal crystal grains 35 directly or through a pinhole andthe like of the non-magnetic oxide 34. In this structure, theferromagnetic metal crystal grains 35 are magnetically coupled.Therefore, the composite magnetic layer 6 shows a soft ferromagnetismand a metal electrical conductivity. Also, in this structure, if theferromagnetic material is at least one selected from the groupconsisting of Co, Fe, and Ni, the non-magnetic material is exemplifiedby Al, Si, Mg, and Ti. For instance, when CoFe is used as the metalferromagnetic substance of the composite magnetic layer 6, and any ofAlO_(x), SiO_(x), MgO_(x), and TiO_(x) is used as the oxide in thecomposite magnetic layer 6, the composite magnetic layer 6 has thestructure as shown in FIG. 5.

FIG. 6 is a cross sectional view of the composite magnetic layer 6 in athird example. This composite magnetic layer 6 has the structure inwhich there are a plurality of pillar-shaped ferromagnetic metal crystalgrains 35 a as crystal grains of the metal ferromagnetic substance, andnon-magnetic oxides 34 a of non-crystal precipitated in the grainboundaries between the ferromagnetic metal crystal grains 35 a. In thiscase, the plurality of ferromagnetic metal crystal grains 35 a passthrough the composite magnetic layer 6 in the direction of thethickness. That is, any of the plurality of ferromagnetic metal crystalgrains 35 a is not separated by the non-magnetic oxide 34 a in thedirection perpendicular to the film surface of the composite magneticlayer 6.

Such a structure can be attained when the non-magnetic material is mixedin the ferromagnetic material in a low density or when the thickness ofthe composite magnetic layer 6 is thinner than a thickness correspondingto the size of the ferromagnetic metal crystal grain 35 in the compositemagnetic layer 6 in case of the second example. The non-magnetic oxide34 a is an oxide of the element selected from among Al, Si, Mg, Ti, Ta,Hf, Zr, Nb, and Ce. In this case, the non-magnetic oxide 34 a segregatesin the crystal grain boundary of the ferromagnetic metal crystal grain35 a. The ferromagnetic metal crystal grain 35 a is not separated in thedirection perpendicular to the film surface of the composite magneticlayer 6. However, the diffusion through the crystal grain boundaries(the non-magnetic oxide 34 a) contributes largely to the Mn diffusion.Therefore, the effect of prevention of the Mn diffusion by the compositemagnetic layer 6 can be obtained enough. In this case, a part of theplurality of ferromagnetic metal crystal grains 35 a is not completelyisolated, and is contact with adjacent one or more of the ferromagneticmetal crystal grains 35 a directly or through a pinhole and the like ofthe non-magnetic oxide 34 a.

In common to the second and third examples of the composite magneticlayer, it is preferable that the thickness of the non-magnetic oxide 34or 34 a is thinner than the particle diameter of the ferromagnetic metalcrystal grain 35 or 35 a and is equal to or less than 2 nm, so that theelectric and magnetic coupling of the ferromagnetic metal crystal grains35 and 35 a can be kept. In this case, the average diameter of theplurality of ferromagnetic metal crystal grains 35 or 35 a is preferablyequal to or less than 10 nm. Moreover, the particle size is preferablyequal or less than 3 nm so that the ferromagnetic metal crystal grain 35or 35 a is not electrically and magnetically isolated completely. Thethickness of the ferromagnetic metal crystal grain 35 or 35 a, and thesize of the non-magnetic oxides 34 or 34 a can be controlled inaccordance with a ratio of the non-magnetic material mixed in theferromagnetic material used for the composite magnetic layer 6, or inaccordance with a film forming condition of the composite magnetic layer6 (a flow rate of gas such as oxygen to be doped in the film formation).The plurality of crystal grains in the composite magnetic layer in thepresent invention keep the ferromagnetic coupling.

In any structures shown in FIG. 4 to FIG. 6, the composite magneticlayer 6 has a structure in which the diffusion can be prevented byscrupulosity of the non-magnetic oxide contained in the compositemagnetic layer 6. In addition, the composite magnetic layer 6 containingthe oxide operates to trap Mn that is easy to be bounded with oxygen.When Mn is diffused into the composite magnetic layer 6 containing theoxide, the diffused Mn is bounded with oxygen and stabilized, and fixedin the composite magnetic layer 6. In addition, the composite magneticlayer 6 hardly has a crystal grain boundary of a normal metalferromagnetic layer, or the crystal grain boundary, which is thehigh-rate diffusion path, is occupied by the oxide and is decreased.Therefore, the diffusion prevention ability is high. Due to theseeffects, the composite magnetic layer 6 can prevent the diffusion of Mninto the tunnel insulating layer 9 effectively without separatingelectrically and magnetically coupling in the pinned ferromagnetic layer20. Such a property cannot be shown in the conventional oxide diffusionpreventing layer.

FIG. 12 shows a configuration of the magneto-resistance device accordingto the third embodiment of the present invention. Referring to FIG. 12,the magneto-resistance device in the third embodiment is different fromthat of the first embodiment shown in FIG. 2 in that themagneto-resistance device in the third embodiment has no compositemagnetic layer 6, and a composite magnetic layer 15 is provided betweenthe metal ferromagnetic layer 8 and the tunnel insulating layer 9 as apart of the free ferromagnetic layer 21 a. The other components are thesame as those of the device shown in FIG. 2. In the magneto-resistancedevice in the third embodiment, the diffusion of Ni that is used in thefree ferromagnetic layer 21 can be prevented by inserting the compositemagnetic layer 15 having the same structure as the composite magneticlayer 6 in the free ferromagnetic layer 21.

In this case, the composite magnetic layer 15 has the same configurationas the composite magnetic layer 6. Like the composite magnetic film 6,the diffusion of Ni can be prevented by the diffusion preventionfunction of the composite magnetic layer 15. That is, the structureshown in FIG. 12 is preferable in the point that the diffusion of Niinto the tunnel insulating layer 9 can be prevented while the MR ratiois increased.

As described above, in the magneto-resistance element 23 of the presentinvention, the composite magnetic layer 6 and the composite magneticlayer 15 are respectively inserted in the pinned ferromagnetic layer 20and the free ferromagnetic layer 21 as diffusion preventing layers.Therefore, a problem of the increase of saturation magnetization may becaused by inserting the composite magnetic layer 6 and the compositemagnetic layer 15. To solve this, the configurations shown in FIG. 13and FIG. 14 should be applied.

FIG. 13 shows a configuration of the magneto-resistance device accordingto the fourth embodiment of the present invention. In the pinnedferromagnetic layer 20, as shown in FIG. 13, a metal ferromagnetic layer7 is provided in the pinned ferromagnetic layer 20 containing acomposite magnetic layer 6 to anti-ferromagnetically couple through thenon-magnetic layer 14. FIG. 14 shows a configuration of themagneto-resistance device according to the fifth embodiment of thepresent invention. As shown in FIG. 14, a metal ferromagnetic layer 8 isprovided in the free ferromagnetic layer 21 b containing the compositemagnetic layer 15 to anti-ferromagnetically couple through thenon-magnetic layer 13.

The non-magnetic layers 14 and 13 are formed of material such that thecomposite magnetic layer 6 and the metal ferromagnetic layer 7, or thecomposite magnetic layer 15 and the metal ferromagnetic layer 8 areanti-ferromagnetically coupled strongly. That is, the non-magneticlayers 14 and 13 are typically formed of any of Cu, Cr, Rh, Ru, andRuO_(x). The pinned ferromagnetic layer 20 is formed from twoferromagnetic layers (the composite magnetic layer 6 and the metalferromagnetic layer 7) and the non-magnetic layer 14, which issandwiched by the two ferromagnetic layers and is anti-ferromagneticallycoupled with the two ferromagnetic layers, so that a substantialmagnetization of the pinned ferromagnetic layer 20 can be reduced.Moreover, the free ferromagnetic layer 21 is configured of twoferromagnetic layers (the composite magnetic layer 15 and the metalferromagnetic layer 8) and the non-magnetic layer 13, which issandwiched by the two ferromagnetic layers and anti-ferromagneticallycoupled with he two ferromagnetic layers. Thus, the non-magnetic layer14 functions to reduce a substantial magnetization or demagnetizationfield in the free ferromagnetic layer 21. A reverse magnetic field ofthe free ferromagnetic layer 21 (coercive force) is decreased throughthe reduction of the demagnetization field. Therefore, the structureshown in FIG. 14 contributes to increase the MR ratio and can prevent Nifrom diffusing into the tunnel insulating layer 9. In addition, the freeferromagnetic layer 21 can be made softer.

In the structure shown in FIG. 14, when the free ferromagnetic layer 21soft enough is obtained, the structure having no soft ferromagneticlayer 10 is made applicable. By excluding the soft ferromagnetic layer10, Ni is excluded from the free ferromagnetic layer 21, and an adverseeffect due to the diffusion of Ni can be fundamentally avoided.

Next, a manufacturing method of the magneto-resistance element of thepresent invention will be described. A TMR element of themagneto-resistance device shown in FIG. 2 is formed by using high vacuumspattering apparatus. Here, an argon pressure in the sputteringdischarge is set to an optimum value in a range of 5 to 10 mTorr, and atarget voltage is set to an optimum value in a range of 300 to 500 V,based on a film to be formed.

First, a Si single crystal substrate having a surface oxide film isprepared as a substrate 1. A Ta layer is formed to have the filmthickness of 3 nm as a lower electrode seed layer 2. Subsequently, A Culayer having the film thickness of 50 nm is formed on the lowerelectrode seed layer 2 as a lower electrode layer 3. Then, a Ta layerhaving the film thickness of 15 nm is formed on the lower electrode 3 asa buffer layer 4. Further, Co₉₀Fe₁₀ having the film thickness of 3 nm isformed. These films have a function to promote orientation to theanti-ferromagnetic phase of the anti-ferromagnetic layer 5 to be formedthereon, and are formed depending on a coupling with theanti-ferromagnetic layer 5.

Next, a Pt₄₉Mn₅₁ film having the film thickness of 30 nm is formed onthe buffer layer 4 as an anti-ferromagnetic layer 5. NiMn and IrMnlayers may be used, which have high thermal stability, as otheranti-ferromagnetic layers 5. Then, a composite magnetic layer 6 havingthe film thickness of 4 nm is formed on the anti-ferromagnetic layer 5as a Mn diffusion preventing layer 6. Details of the method of formingthe composite magnetic layer 6 will be described later. Next, a Co₉₀Fe₁₀film having the film thickness of 5 nm is formed as a metalferromagnetic layer 7. Subsequently, an Al layer having the filmthickness of 2 nm is formed on the metal ferromagnetic layer 7 as atunnel insulating layer 9. Then, a plasma oxidation (a high frequencyplasma oxidation method) is carried out in an oxygen atmosphere to forman AlO_(x) layer. It should be noted that the tunnel insulating layer 9may be formed from an AlN_(x) layer or a MgO_(x) layer.

Next, a Co₉₀Fe₁₀ film having the film thickness of 2.5 nm is formed onthe tunnel insulating layer 9 as the metal ferromagnetic layer 8.Subsequently, a NiFe film having the film thickness of 7.5 nm is formedas a soft magnetic layer 10. Subsequently, a Ta layer having the filmthickness of 30 nm is formed on the soft magnetic layer 10 as anelectrode contact layer 11. Thereafter, a sample is taken out from achamber, and a photo lithography, an etching, and a deposition of theinterlayer insulation film are carried out to form connection patternsor contact holes. Then, the sample is carried in an upper electrode filmforming apparatus. After the surface of the contact is cleaned in avacuumed state through the Ar etching, a Cu layer is formed to have thefilm thickness of 300 nm. Finally. The sample is taken out from thechamber, and the pattern of an upper electrode 12 is formed through thephoto lithography and the etching.

The TMR element as the magneto-resistance device is completed throughthe above-mentioned process.

The composite magnetic layer 6 can be manufactured by a reactivesputtering using a sputtering gas which contains an oxygen gas, as wellas the composite magnetic layer 15. A mixed gas of the oxygen gas andthe argon gas is typically used as the sputtering gas. As a sputteringtarget, typically, an alloy is used that is formed of a metalferromagnetic substance and a non-magnetic element that can be easilyoxidized compared with the metal ferromagnetic substance. For example,(Co₉₀Fe₁₀)₈₅Ta₁₅ alloy target is used. When this alloy target issputtered by using the sputtering gas which contains the oxygen gas,oxygen is bounded with the non-magnetic metal (Ta) prior to the metalferromagnetic substance (Co₉₀Fe₁₀). By adjusting an amount of the oxygencontained in the sputtering gas appropriately, only the non-magneticmetal is oxidized without oxidizing the metal ferromagnetic substance,and the composite magnetic layer 6 can be formed.

FIG. 7 is a graph showing resistivity of a thin film (vertical axis)that is formed by sputtering the (Co₉₀Fe₁₀)₈₅Ta₁₅ alloy target, which isformed of CoFe as the ferromagnetic substance and Ta as the non-magneticelement, using the sputtering gas containing the oxygen gas. FIG. 8 is agraph showing a saturation magnetization of the formed thin film(vertical axis). The horizontal axes in these graphs indicate a ratio ofa flow rate the oxygen gas (sccm) to a flow rate of the argon gas(sccm), which are introduced into the chamber in which the sputtering iscarried out (hereafter, to be referred to as a “oxygen/argon flow rateratio”). A main portion of the formed thin film was an oxide amorphouslayer having the composition of (CoFe)_(Y)Ta_(1-Y)O_(x), and the CoFepillar-shaped crystal grains are formed partially in the formed thinfilm. That is, the structure of the thin film is such as shown in FIG.4. As shown in FIGS. 7 and 8, when the oxygen/argon flow rate ratio issmall, the thin film shows a metal electrical conductivity and asaturation magnetization is large. When the oxygen/argon flow rate ratioexceeds 0.2, the resistivity of the thin film increases rapidly, and thesaturation magnetization decreases rapidly.

These graphs show that it is necessary that the oxygen/argon flow rateratio is less than 0.2 in order that CoFe contained in the thin filmexists in a metal state. This inference has been proven by the analysisusing XPS (X-ray Photoelectron Spectroscopy).

FIG. 9 indicates Co_(2p) spectra obtained by carrying out XPS analysison the thin films formed under the condition of the oxygen/argon flowrate ratios of 0.13 and 0.54. In the Co_(2p) spectra in FIG. 9, 70percent or more Co is in a metal state in the thin film when theoxygen/argon flow rate ratio is 0.13, and Co contained in the thin filmis oxidized when the oxygen/argon flow rate ratio is 0.54.

The above-mentioned phenomena will be described as follows. Oxygen inthe reactive sputtering is easy to be bounded with Ta, compared withCo₉₀Fe₁₀, and as a result, Ta is selectively oxidized first. When theoxygen/argon flow rate ratio is increased, Ta is oxidized completely andbecomes Ta₂O₅ in the oxygen/argon flow rate ratio of approximately 0.2.Then, the oxidation of Co₉₀Fe₁₀ is started. (Co₉₀Fe₁₀)—O_(x), which isobtained by oxidizing Co₉₀Fe₁₀, is an anti-ferromagnetic insulator.Therefore, the magnetization decreases, and the resistance increasesrapidly. Thus, CoFe loses the electrical conductivity and theferromagnetism if it is not in metal state. For this reason, theoxygen/argon flow rate ratio in the reactive sputtering should be equalto or less than 0.2. Moreover, as understood from FIG. 7, theresistivity of the composite magnetic layer at that time is in a rangeof 10 to 3000 μΩcm. In other word, if it is below 3000 μΩcm, theelectrical conductivity and the ferromagnetism enough to themagneto-resistance element can be obtained. That is to say, when CoFe isused as the metal ferromagnetic substance, and any one of TaO_(x),HfO_(x), NbO_(x), ZrO_(x), AlO_(x), MgO_(x) and SiO_(x) is used as theoxide of the non-magnetic metal, the composite magnetic film 6 can beformed of CoFe in the metal state if the oxygen/argon flow rate ratio isless than 0.2.

When the film is formed under the condition that (Co₉₀Fe₁₀)₈₅Ta₁₅ alloytarget is used, the flow rate of argon is 11.5 sccm, and the flow rateof oxygen is 1.5 sccm (oxygen/argon flow rate ratio=0.13), CoFeTaO_(x)composite magnetic film 6 of the magneto-resistance device shown in FIG.2 has such a structure that the amorphous phase occupies in major and apillar-shaped crystalline phase is partially contained. That is, theCoFeTaO_(x) composite magnetic film 6 has the structure shown in FIG. 4.This has been confirmed by a transmission type electron microscope. Atthis time, the composition of the amorphous phase is Co₃₈Fe₅Ta₇O₅₀.

In the composite magnetic layer 6 having such features as in the presentinvention, the composition ratio of the ferromagnetic material CoFe andthe non-magnetic material Ta in the amorphous phase is important. Forinstance, in case of more Ta, the CoFe cluster in the amorphous phase isisolated in magnetically and electrically. The resistance increasesremarkably when it is isolated electrically. When it is isolatedmagnetically, a magnetic coupling becomes weak with the Co₉₀Fe₁₀ layer(metal ferromagnetic layer 7) and the Pt₄₉Mn₅₁ layer (anti-ferromagneticlayer 5) that are formed on up and down sides of the composite magneticlayer 6. Thus, the magnetization of the Co₉₀Fe₁₀ layer is not fixed. Onthe other hand, when Ta is few, an enough effect of the diffusionprevention is not achieved.

From the above-mentioned veiwpoints, it is preferable that anappropriate composition ratio of Ta (the non-magnetic oxide material) toCoFe (the ferromagnetic material) in the amorphous phase is in a rangefrom 10% to 40%. Moreover, in order to obtain the composite magneticlayer 6 of the above-mentioned amorphous phase, the atomic radius of thenon-magnetic material should be larger than that of the ferromagneticmaterial, and the thermal stability of the oxide has to be high. Suchnon-magnetic material is Zr, Hf, Nb, and Ce, besides Ta. The compositionratios of the ferromagnetic material and the non-magnetic material canbe controlled based on the composition ratio of the sputtering target,and deposition conditions of the sputtering power and the argon pressureand the like.

In Japanese Laid Open Patent Application (JP-P2002-158381A), it isdescribed that an amorphous phase is used in fixed layers even in themagneto-resistance element. However, in the present invention, the oxidewith high thermal stability such as TaO_(x), ZrO_(x), NbO_(x), HfO_(x),and CeO_(x) is used as the non-magnetic material in the amorphous,unlike the above Japanese Laid Open Patent Application. That is to say,the amorphous structure is not essentially important for the effect ofprevention of the Mn diffusion in the present invention, which will bedescribed below referring to FIG. 10.

FIG. 10 is a graph showing a relation between an amount of the Mndiffusion and thermal treatment temperature. The vertical axis is theamount of the diffusion amount of Mn from the anti-ferromagnetic layer 5to tunnel insulation film 9 (based on photoelectric spectrum). Thehorizontal axis is the thermal treatment temperatures of samples. FIG.10 shows measurement data of the amounts of the Mn diffusions in samples1 and 2. The sample 1 has a structure from the substrate 1 to the tunnelinsulation film 9, in which structure a usual amorphous film(Co₉₀Fe₁₀)₈₅Ta₁₅ is used in the pinned ferromagnetic layer 20 (shown inthe graph as “Comparison example” by a broken line). The sample 2 has astructure from the substrate 1 to the tunnel insulation film 9, in whichstructure CoFeTaO_(x) composite magnetic layer 6 of the presentinvention is used in the pinned ferromagnetic layer 20 (shown in thegraph as “Experiment example” by a solid line). The samples have thefollowing structure. As described above, each of the samples has thestructure in which substrate/lower electrode seed layer/bufferlayer/anti-ferromagnetic layer/usual non-oxidation amorphous film orcomposite magnetic layer/metal ferromagnetic layer/tunnel insulatinglayer in order (the lower electrode layer is omitted).

(1) Sample 1 (the Comparison Example as a Conventional Example)

Substrate/Ta (3 nm)/Ni₈₁Fe₁₉ (3 nm)/Ir₂₀Mn₈₀ (10 nm)/(Co₉₀Fe₁₀)₈₅Ta₁₅ (3nm)/Co₉₀Fe₁₀ (3 nm)/Al (1 nm)-O_(x)

(2) Sample 2 (the Experiment Example of the Present Invention)

Substrate/Ta (3 nm)/Ni₈₁Fe₁₉ (3 nm)/Ir₂₀Mn₈₀ (10 nm)/CoFeTaO_(x) (3nm)/Co₉₀Fe₁₀ (3 nm)/Al (1 nm)-O_(x)

As shown in FIG. 10, in the composite magnetic layer 6 of the presentinvention (sample 2), the diffusion amount of Mn is always low, comparedwith the conventional non-oxidation amorphous film (sample 1). In thethermal treatment at 400° C., the diffusion amount of Mn is suppressedeven to 60% (50% or less at 350° C.), compared with the non-oxidationamorphous. This is the effect that Mn is prevented from diffusing in thepinned ferromagnetic layer 20 by the oxide.

The composite magnetic film 6 can be formed by direct sputtering byusing the oxide target of CoFeTaO_(x), in addition to theabove-mentioned reactive sputtering method. In that case, to supplementoxygen loss in the sputtering film, the oxygen gas may be mixed in thesputtering atmosphere. In the direct sputtering of the oxide target, itis preferable that the manufacturing throughput and controllability canbe improved. The composite magnetic layer CoFeTaO_(x) layer describedabove has the structure shown in FIG. 4 that is formed of the amorphousphase 32 and the pillar-shaped crystalline phase 33.

As shown in FIG. 5, the second composite magnetic layer 6 includes aplurality of ferromagnetic metal crystal grains 35 formed of theferromagnetic material. The crystal grains are separated by thenon-magnetic oxides 34 and a part of the crystal grains of the pluralityof ferromagnetic metal crystal grains 35 is contact with one or morecrystal grains of the other adjacent crystal grains. Such a structurecan be achieved when the oxide such as the oxide of Al, Si, Mg, or Ti,which is thermally stable and non-solid-soluble in the ferromagneticmaterial, and whose atomic radius is smaller than that of theferromagnetic element is used as the non-magnetic material. Thenon-magnetic oxide 34 between the crystal grains has an ununiformthickness, and has a partial thin portion and pinholes. The thickness ispreferably 2 nm or less. In such a structure, the ferromagnetic metalcrystal grain 35 is not an isolated grain and a plurality of crystalgrains contacts with each other in some place. The size and shape of thecrystal grains are ununiform. The average crystal grain diameter can beestimated by X-ray diffractometer or an electron diffractometer. Throughthese measurements, it was found that the average diameter of theferromagnetic metal crystal grains 35 in the composite magnetic layer 6is 10 nm or less, unlike the usual ferromagnetic metal crystal grain(the average diameter is 15 to 30 nm). This is because a grain growth ofthe ferromagnetic metal crystal grain 35 is suppressed with thenon-magnetic oxide 34.

The composite magnetic layer 6 in the second example is possible to bemanufactured by the same method as the above-mentioned CoFeTaO_(x). Thatis, when being manufactured by the reactive sputtering, the compositionratio of the ferromagnetic material and the non-magnetic material in thesputtering target is kept appropriate, the flow rate of oxygen isoptimized so that the non-magnetic material is oxidize completely, andthe most part of the ferromagnetic material is in a metal state. Thus,the deposition of the layer is achieved.

Also, when the ratio of the non-magnetic material to the ferromagneticmaterial in the sputtering target is increased, the ferromagnetic metalcrystal grain 35 in the composite magnetic layer 6 becomes small, andthe thickness of the non-magnetic oxide 34 between the grain boundariesincreases. When the thickness of the non-magnetic oxide 34 becomesthick, the adjacent grains are separated from each other completely bythe non-magnetic oxide 34, so that the coupling between theferromagnetic metal crystal grains 35 is broken magnetically andelectrically. At this time, the composite magnetic layer shows asuper-paramagnetism due to thermal fluctuation, and becomes insulative.Therefore, the composition ratio of the sputtering target is determinedsuch that the magnetic and electric coupling between the adjacentferromagnetic metal crystal grains 35 are not broken, by adjusting thecomposition of the sputtering target and the flow rate of oxygen. Thecomposition ratio of the non-magnetic material to the ferromagneticmaterial is preferably equal to or less than 40%.

As shown in FIG. 6, the composite magnetic layer 6 in the third exampleincludes a plurality of pillar-shaped ferromagnetic metal crystal grains35 a and non-magnetic oxides 34 a. The plurality of ferromagnetic metalcrystal grains 35 a are separated by the non-magnetic oxide 34 a fromeach other. The crystal grain boundaries in the structure in thedirection perpendicular to the film surface of the composite magneticlayer 6 are not separated by the nonmagnetic oxide 34 a. Such astructure can be achieved when the thickness of the composite magneticlayer 6 is thinner than the size of the ferromagnetic metal crystalgrain 35 a, or when the ratio of the non-magnetic material to be mixedin the composite magnetic layer 6 is low (roughly the composition ratioof 10% or less). Any of oxides of Ta, Hf, Zr, Nb, Al, Si, Mg, and Ti canbe applicable as the non-magnetic material.

In these composite magnetic layers 6, the anti-ferromagnetic layer 5 andthe tunnel insulating layer 9 are not completely separated by thenon-magnetic oxide 34 a. However, a region, which is formed between thecrystal grain boundaries in the pinned ferromagnetic layer 20, andthrough which Mn is diffused easily, is buried by the non-magnetic oxide34 a. Therefore, an enough effect of the diffusion prevention can beobtained. Also, the advantages of the composite magnetic layer 6 in thethird example is in that simplification and thinning of the pinnedferromagnetic layer 20 can be obtained while keeping the prevention ofthe Mn diffusion. Also, it is in that the grain growth from the lowerlayer can be maintained. In this composite magnetic layer 6, thenon-magnetic oxide 34 is segregated in the grain boundary. Therefore,the most portion of the interface contacted with the tunnel insulatinglayer 9 is the ferromagnetic metal crystal grains 35 a even if thecomposite magnetic layer 6 is directly contact with the interface of thetunnel insulating layer 9. Thus, the high MR ratio can be maintained. Itis not necessary to insert the metal ferromagnetic layer 7 between thecomposite magnetic layer 6 and the tunnel insulating layer 9, in orderto keep the high MR ratio. Therefore, the pinned ferromagnetic layer 20can be formed only from the composite magnetic layer 6. Moreover, theferromagnetic metal crystal grains 35 a in the composite magnetic layer6 are not separated by the non-magnetic oxide 34 a. Therefore, thecrystal orientation can be transferred to the upper layer. This propertyis effective in a spin valve structure, in which the anti-ferromagneticlayer 5 is arranged above the tunnel insulating layer 9, since thecomposite magnetic layer 6 arranged below the anti-ferromagnetic layer 5promotes the crystal orientation of the anti-ferromagnetic layer 5 andgenerates an excellent exchange bias characteristic.

In the measurement of a single-layer film of CoFeTaO_(x) formed asmentioned above and a single-layer film of CoFeAlO_(x) (formed bysputtering a (Co₉₀Fe₁₀)₇₈Al₂₂ target (oxygen/argon flow rate ratio=0.07)in a mixture atmosphere of argon and oxygen), the resistivity is 85 μΩcmand 810 μΩcm, respectively. The magnetization measurement shows that thecoercive forces are respectively 2 Oe and 5 Oe and ferromagnetichysteresis curves are obtained in proper rectangular shapes. The resultof the X-ray diffraction on these single-layer films shows that only asmall diffraction peak due to the pillar-shaped crystalline region wasobserved in case of CoFeTaO_(x), while the diffraction peaks of theface-centered cubic lattice were observed in case of CoFeAlO_(x) and theaverage crystal grain diameter calculated from the half width using theDebye Sierra formula is approximately 6 nm. Consequently, the averagediameter is 6 nm in the CoFeAlO_(x) film and shows ferromagneticproperties and metal conductive properties. Therefore, it could beconsidered that the grains are partially contact with each other.

FIG. 11 is a graph showing a magnetization curve of the exchangecoupling film as the anti-ferromagnetic layer 5 containing the diffusionpreventing layer/the pinned ferromagnetic layer 20. The vertical axis ismagnetization, and the horizontal axis is magnetic field. Here, a sample3 (“Comparison example” shown by the solid line in the graph) has theexchange coupling film including the pinned ferromagnetic layer 20 witha non-magnetic oxide layer of Ta (0.5 nm)-Ox as the diffusion preventingfilm (metal ferromagnetic layer 7/non-magnetic oxide layer/metalferromagnetic layer 7). A sample 4 (“Experiment example” shown by thebroken line in the graph) has the exchange coupling film including thepinned ferromagnetic layer 20 with a CoFeTaO_(x) layer of the presentinvention as the composite magnetic layer 6 (composite magnetic layer6/metal ferromagnetic layer 7). Thermal treatment is carried out on thesamples in the magnetic field of 400° C.

Here, each sample will be described in the order of substrate/lowerelectrode seed layer/buffer layer/anti-ferromagnetic layer/non-oxidizedamorphous film or composite magnetic layer/usual metal ferromagneticlayer/tunnel insulating layer (the lower electrode layer is omitted.)

(3) Sample 3 (Comparison Example to the Conventional Example)

Substrate/Ta (3 nm)/Co₉₀Fe₁₀ (3 nm)/Pt₄₉Mn₅₁ (30 nm)/Co₉₀Fe₁₀ (3 nm)/Ta(0.5 nm)-O_(x)/Co₉₀Fe₁₀ (5 nm)/Al (2 nm)-O_(x)

(4) Sample 4 (Experiment Example of the Present Invention)

Substrate/Ta (3 nm)/Co₉₀Fe₁₀ (3 nm)/Pt₄₉Mn₅₁ (30 nm)/CoFeTaO_(x) (3nm)/Co₉₀Fe₁₀ (5 nm)/Al (2 nm)-O_(x)

In the sample 3, the exchange coupling magnetic field becomes 0 Oe andthe pinned layer is not fixed though the Ta—Ox (0.5 nm) layer isextremely thin. This could be considered as the result that the magneticcoupling is broken by Ta (0.5 nm)-Ox layer. On the other hand, in thesample 4 (the present invention), an exchange bias is generated in thepinned ferromagnetic layer 20 and the exchange coupling magnetic fieldHex is 130 Oe. In the present invention, it is possible that the oxide(the composite magnetic layer 6) functioning as the diffusion preventinglayer is contained in the pinned ferromagnetic layer 20 while keepingthe magnetic coupling of the pinned ferromagnetic layer 20 and theanti-ferromagnetic layer 5.

The composite magnetic layer 15 can be similarly used to prevent the Nidiffusion from a Ni-based soft magnetic layer in the free ferromagneticlayer. However, when the composite magnetic layer 15 has softferromagnetism enough, the soft ferromagnetic layer 10 is not necessaryin the third embodiment shown in FIG. 12. That is, the compositemagnetic layer 15 (having the structure as shown in FIG. 4) is formed ofmetal ferromagnetic substance, which has been not oxidized, as a maincomponent and oxide of a non-magnetic element easy to bind with oxygencompared with the metal ferromagnetic substance, as a sub component. Inthe composite magnetic layer 15, the ferromagnetic metal crystal grainsbecome small and the crystal magnetic anisotropy decreases. For thisreasons, it becomes relatively magnetically soft. In this case, Ni isnot diffused into the tunnel insulating layer 9.

The composite magnetic layer 15 contains many non-magnetic elements.Therefore, there is a possibility that the MR ratio becomes small if thecomposite magnetic layer 15 is arranged directly on the tunnelinsulating layer 9. For this reason, the high MR ratio is kept byarranging the metal ferromagnetic layer 8 between the composite magneticlayer 15 and the tunnel insulating layer 9. It is preferable that themetal ferromagnetic layer 8 is formed of a ferromagnetic alloycontaining Co as the main component, and is typically formed of CoFe.The composite magnetic layer 15 is formed as a composite thin film mixedwith a ferromagnetic substance without Ni (typically, CoFe), and theoxide of a non-magnetic metal. In the free ferromagnetic layer 21 havingsuch a structure, the high MR ratio can be attained by arranging themetal ferromagnetic layer 8 formed of the material with high spinpolarization and thermal stability directly on the tunnel insulatinglayer 9. In addition, the composite magnetic layer 15 soft magneticallyaffects the exchange interaction to the metal ferromagnetic layer 8 tomake the metal ferromagnetic layer 8 soft, and as the result of this,the free ferromagnetic layer 21 is made to be soft wholly.

Also, in the composite magnetic layer 6 in the third example (thestructure shown in FIG. 6), most of the elements that contact theboundary are a ferromagnetic element as mentioned above. Therefore, thecomposite magnetic layer 6 can be arranged directly on the boundary ofthe tunnel insulating layer 9, and the metal ferromagnetic layer 8 isnot necessary in the above-mentioned case. In this case, the softferromagnetic layer 10 is formed of the ferromagnetic substancecontaining Ni, typically, NiFe and is provided on the composite magneticlayer 15. The composite magnetic layer 15 as the above-mentionedcomposite thin film shows an effect of the prevention of Ni diffusion.Therefore, the diffusion of Ni contained in the soft ferromagnetic layer10 into the tunnel insulating layer 9 can be prevented by the compositemagnetic layer 15. The structure is preferable in that Ni can beprevented from diffusing into the tunnel insulating layer 9 whileincreasing the MR ratio.

By adopting the configuration of the magneto-resistance device shown inFIG. 12, it is possible to achieve the prevention of Ni diffusion fromthe soft magnetic layer at the same time as prevention of Mn diffusion.Thus, higher thermal resistance can be achieved. Since the samediffusion preventing layer can be used, the manufacturing method is easyeven if the manufacturing cost is considered. In order to obtain thethermal resistance up to approximately 400° C. in the magneto-resistancedevice, the diffusion of Mn from the anti-ferromagnetic layer and Nifrom the free ferromagnetic layer needs to be prevented at the sametime, as mentioned above. Therefore, it is effective that the compositemagnetic layer is provided as a diffusion preventing layer in the fixedferromagnetic layer and the free ferromagnetic layer.

EXPERIMENT 1

The magneto-resistance device of the present invention having theabove-mentioned configuration was manufactured by the above-mentionedmethod. The result of the experiment shows improvement of the thermalstability and the like due to the introduction of the composite magneticfilm. That will be described below with reference to FIG. 15.

FIG. 15 is graphs showing the relation between thermal treatmenttemperature and MR ratio in the magneto-resistance device. The verticalaxis shows the MR ratio (%), and the horizontal axis shows the thermaltreatment temperatures (° C.). Here, each of samples will be describedbelow.

(5) Sample 5 (Comparison Example to the Conventional Example)

Substrate/Ta (3 nm)/Cu (50 nm)/Ta (15 nm)/Co₉₀Fe₁₀ (3 nm)/Pt₄₉Mn₅₁ (30nm)/Co₉₀Fe₁₀ (9 nm)/Al (2 nm)-O_(x)/Co₉₀Fe₁₀ (2. nm)/Ni₈₁Fe₁₉ (7.5nm)/Ta (30 nm)/Cu (300 nm).

Here, the sample is formed in the order of substrate/lower electrodeseed layer/lower electrode layer/buffer layer/anti-ferromagneticlayer/metal ferromagnetic layer/tunnel insulating layer/metalferromagnetic layer/soft magnetic layer/electrode electric contactlayer/upper electrode layer.

(6) Sample 6 (Experiment Example of the Present Invention)

Substrate/Ta (3 nm)/Cu (50 nm)/Ta (15 nm)/Co₉₀Fe₁₀ (3 nm)/Pt₄₉Mn₅₁ (30nm)/CoFeTaO_(x) (4 nm)/Co₉₀Fe₁₀ (5 nm)/Al (2 nm) O_(x)/Co₉₀Fe₁₀ (2.5nm)/Ni₈₁Fe₁₉ (7.5 nm)/Ta (30 nm)/Cu (300 nm).

Here, the sample is formed in the order of substrate/lower electrodeseed layer/lower electrode layer/buffer layer/anti-ferromagneticlayer/composite magnetic layer/metal ferromagnetic layer/tunnelinsulating layer/metal ferromagnetic layer/soft magnetic layer/electrodeelectric contact layer/upper electrode layer.

(7) Sample 7 (Example of Experimenting on the Present Invention)

Substrate/Ta (3 nm)/Cu (50 nm)/Ta (15 nm)/Co₉₀Fe₁₀ (3 nm)/Pt₄₉Mn₅₁ (30nm)/CoFeTaO_(x) (4 nm)/Co₉₀Fe₁₀ (5 nm)/Al (2 nm)-O_(x)/Co₉₀Fe₁₀ (1nm)/CoFeTaO_(x) (3 nm)/Ni₈₁Fe₁₉ (7.5 nm)/Ta (30 nm)/Cu (300 nm)

Here, the sample is formed in the order of substrate/lower electrodeseed layer/lower electrode layer/buffer layer/anti-ferromagneticlayer/composite magnetic layer/metal ferromagnetic layer/tunnelinsulating layer/metal ferromagnetic layer/composite magnetic layer/softmagnetic layer/electrode electric contact layer/upper electrode layer.

The composite magnetic layer CoFeTaO_(x) in these samples is formed byreactive sputtering (the oxygen/argon flow rate ratio=0.13) by using thealloy target of (Co₉₀Fe₁₀)₈₅Ta₁₅. It was confirmed that the resistivityof this composite magnetic film is 85 μΩcm and coercive force is 25 Oeof the ferromagnetic by a sheet resistance measurement and a magneticmeasurement.

The sample 5 is the conventional exchange bias type magneto-resistancedevice. The sample 6 is the magneto-resistance device of the presentinvention in which the diffusion of Mn is prevented by using theCoFeTaO_(x) composite magnetic layer 6. The sample 7 is themagneto-resistance device of the present invention in which thediffusion of Mn and Ni is prevented by using the CoFeTaO_(x) compositemagnetic layers 6 and 15 in the pinned ferromagnetic layer and the freeferromagnetic layer.

In the sample 5, the MR ratio becomes the maximum of 53% at 330° C.However, the MR ratio decreases rapidly at higher temperature. On theother hand, in the sample 6, the MR ratio is kept steadily to 40% ormore at up to 365° C., and the thermal resistance is improved. This isthe effect of the composite magnetic layer CoFeTaO_(x) that prevents theMn diffusion from the anti-ferromagnetic layer.

The sample 7 further improves the thermal resistance, and the MR ratiois kept to 40% or more up to at 390° C. This could be considered as theeffect of the prevention of diffusion of Ni from the free ferromagneticlayer in addition to the prevention of diffusion of Mn from theanti-ferromagnetic layer.

FIG. 16 is graphs showing a magneto-resistance curve of the sample 7after the thermal treatment for one hour at 380° C. The vertical axisshows a MR ratio (%) and the horizontal axis shows a magnetic field(Oe). As seen clearly from FIG. 16, the MR-curve of an excellent spinvalve type can be achieved and there is no problem in the magneticproperty. In this way, in the magneto-resistance device of the presentinvention, in which the composite magnetic layers 6 and 15 are used inthe pinned ferromagnetic layer and the free ferromagnetic layer, thethermal resistance is improved greatly, and thermal resistance of 390°C. at maximum was achieved.

EXPERIMENT 2

The magneto-resistance device is manufactured by the same method as theexperiment example 1 to contain the CoFeAlO_(x) composite magnetic layer6 in the pinned ferromagnetic layer 20. The film structure will bedescribed below with reference to FIG. 17.

FIG. 17 is a table showing relation between MR ratio and exchangecoupling magnetic field. Here, each of samples is as follows.

(8) Sample 8 (Comparison Example to the Conventional Example)

Substrate/Ta (30 nm)/Ni₈₁Fe₁₉ (3 nm)/Ir₂₀Mn₈₀ (10 nm)/Co₉₀Fe₁₀ (12nm)/Al (2 nm)-O_(x)/Co₉₀Fe₁₀ (2.5 nm)/Ni₈₁Fe₁₉ (7.5 nm)/Ta (30 nm)/Cu(300 nm).

Here, the sample was formed in the order of substrate/lower electrodeseed layer/buffer layer/anti-ferromagnetic layer/metal ferromagneticlayer/tunnel insulating layer/metal ferromagnetic layer/soft magneticlayer/electrode electric contact layer/upper electrode layer (the lowerelectrode layer is omitted).

(9) Sample 9 (Experiment Example of the Present Invention)

Substrate/Ta (30 nm)/Ni₈₁Fe₁₉ (3 nm)/Ir₂₀Mn₈₀ (10 nm)/Co₉₀Fe₁₀ (1.5nm)/CoAlO_(x)[A] (8 nm)/Co₉₀Fe₁₀ (1.5 nm)/Al (2 nm)-O_(x)/Co₉₀Fe₁₀ (2.5nm)/Ni₈₁Fe₁₉ (7.5 nm)/Ta (30 nm)/Cu (300 nm).

Here, the sample was formed in the order of substrate/lower electrodeseed layer/buffer layer/anti-ferromagnetic layer/metal ferromagneticlayer/composite magnetic layer/metal ferromagnetic layer/tunnelinsulating layer/metal ferromagnetic layer/soft magnetic layer/electrodeelectric contact layer/upper electrode layer (the lower electrode layeris omitted).

(10) Sample 10 (Experiment Example of the Present Invention)

Substrate/Ta (30 nm)/Ni₈₁Fe₁₉ (3 nm)/Ir₂₀Mn₈₀ (10 nm)/CoFeAlO_(x)[B] (6nm)/Al (2 nm)-O_(x)/Co₉₀Fe₁₀ (2.5 nm)/Ni₈₁Fe₁₉ (7.5 nm)/Ta (30 nm)/Cu(300 nm).

Here, the sample was manufactured in the order of substrate/lowerelectrode seed layer/buffer layer/anti-ferromagnetic layer/compositemagnetic layer/tunnel insulating layer/metal ferromagnetic layer/softmagnetic layer/electrode electric contact layer/upper electrode layer(the lower electrode layer is omitted).

The CoFeAlO_(x) composite magnetic layer A used in the sample 9 wasmanufactured by the reactive sputtering (the oxygen/argon flow rateratio=0.07) by using the (Co₉₀Fe₁₀)₇₈Al₂₂ sputtering target as describedabove. As the result of the X-ray diffraction measurement, the averagecrystal grain diameter is 6 nm, the resistivity is 810 μΩcm showingelectrical conductivity, and the coercive force is 5 Oe showing aferromagnetic hysteresis curve in a proper rectangular shape.

On the other hand, the CoFeAlOx composite magnetic layer B of the sample10 was manufactured by the reactive sputtering (the oxygen/argon flowrate ratio=0.035) by using the alloy target of (Co₉₀Fe₁₀)₉₅Al₅. ThisCoFeAlO_(x) shows a ferromagnetic hysteresis with the coercive force of30 Oe (magnetic measurement), and the resistivity is 20 μΩcm.

The table in FIG. 17 shows relation of MR ratio and the exchangecoupling magnetic field of these magneto-resistance devices (the samples8 to 10) in thermal treatments at 250° C., 300° C., 350° C., and 400° C.The conventional spin valve magneto-resistance device (the sample 8) hasthe high MR ratio of 42% at 250° C. However, the ratio of theconventional spin valve magneto-resistance device (the sample 8) israpidly decreased in the higher temperature, and the thermal resistanceis the worst.

On the other hand, in the sample 9 as the magneto-resistance device ofthe present invention, the CoAlO_(x) composite magnetic layer A isinserted in the pinned ferromagnetic layer 20 to prevent the Mndiffusion. Therefore, even after the thermal treatment in a range of 250to 350° C., the MR ratio is stably kept to a high value. Moreover, theexchange bias magnetic field of 80 to 92 Oe is also generated. In thesample 10 as the magneto-resistance device of the present invention,only the CoFeAlO_(x) composite magnetic layer is used as the pinnedferromagnetic layer 20 without the metal ferromagnetic layer 7. Even inthis case, the MR ratio takes a high value of 40%. Since the pinnedferromagnetic layer 20 is thin, the exchange coupling magnetic field of200 Oe or more is generated. Moreover, the thermal resistance is alsohigh, and the MR ratio is maintained to the value of 33% even after thethermal treatment at 350° C. By using the composite magnetic layer ofthe present invention for the pinned ferromagnetic layer 20, theexchange coupling between the anti-ferromagnetic layer 5 and the pinnedferromagnetic layer 20 is kept, and the Mn diffusion from theanti-ferromagnetic layer 5 can be prevented so that the thermalresistance can be improved.

EXPERIMENT 3

The experimental example 3 of the anti-ferromagnetic coupling film usingthe composite magnetic layer will be described. The samples weremanufactured, in which the Co₉₀Fe₁₀ (6 nm) metal ferromagnetic layer andthe CoFeTaO_(x) (5 nm) composite magnetic layer are ferromagnetically oranti-ferromagnetically coupled. The composite magnetic layer CoFeTaO_(x)(6 nm) was formed by the reactive sputtering (the oxygen/argon flow rateratio=0.13) by using the alloy target of (Co₉₀Fe₁₀)₈₅Ta₁₅ in a mixtureatmosphere of argon and oxygen, and was the same film as the experimentexample 1. After the film growth, thermal treatment at 300° C. wascarried out on the sample in the magnetic field to give the magneticanisotropy. Those magnetization curves (vibratory magnetometer) aredescribed with reference to FIG. 18.

FIG. 18 is a graph showing magnetization curve of each of the samples.The vertical axis shows magnetization (emu) and the horizontal axisshows magnetic field (Oe). Here, each sample was formed as follows.

(11) Sample 11 (Experiment Example of the Present Invention)

Substrate/Ta (1.5 nm)/Co₉₀Fe₁₀ (6 nm)/CoFeTaO_(x) (5 nm)/Al (2nm)-O_(x).

Here, the sample was manufactured in the order of substrate/lowerelectrode seed layer/metal ferromagnetic layer/composite magneticlayer/tunnel insulating layer.

(12) Sample 12 (Experiment Example of the Present Invention)

Substrate/Ta (1.5 nm)/Co₉₀Fe₁₀ (6 nm)/Ru (1.0 nm)/CoFeTaO_(x) (5 nm)/Al(2 nm)-O_(x).

Here, the sample was manufactured in the order of substrate/lowerelectrode seed layer/metal ferromagnetic layer/non-magneticlayer/composite magnetic layer/tunnel insulating layer.

The sample 11 is a laminated film in which a Co₉₀Fe₁₀ film (6 nm) and aCoFeTaO_(x) film (5 nm) are laminated directly and ferromagneticallycoupled. In the sample 12, a Co₉₀Fe₁₀ film (6 nm) and a CoFeTaO_(x) film(5 nm) are laminated through a Ru film (1 nm), and two magnetic layersare anti-ferromagnetically coupled by the effect of the Ru film (1 nm).M1 and M2 shown in FIG. 18 are saturation magnetizations of the Co₉₀Fe₁₀film (6 nm) and the CoFeTaO_(x) film (5 nm), respectively.

In the sample 11, a ferromagnetic hysteresis in a proper rectangularshape can be observed, and the height is M1+M2 (a summation of thesaturation magnetizations in two layers). In the sample 12, a smallhysteresis is observed in the magnetic field of approximately 0, and amagnetization curve without linear hysteresis is observed in a highmagnetic field. This is because the magnetizations of the Co₉₀Fe₁₀ film(6 nm) and the CoFeTaO_(x) film (5 nm) are anti-ferromagneticallycoupled. The height of the ferromagnetic hysteresis in the magneticfield of approximately 0 is M1−M2 as the difference between thesaturation magnetizations of both the ferromagnetic layers. When theapplied magnetic field is increased to a higher value, theanti-ferromagnetic coupling of these Co₉₀Fe₁₀ film (6 nm) andCoFeTaO_(x) film (5 nm) are broken. When the magnetic field ofapproximately 2300 Oe is applied, both the ferromagnetic layers becomeferromagnetically coupled. By using the anti-ferromagnetic coupling filmas in the sample 12, an effective magnetization can be reduced fromM1+M2 to M1−M2 in the low magnetic field. By using theanti-ferromagnetic coupling film for the free ferromagnetic layer or thepinned ferromagnetic layer of the magneto-resistance device so that themagnetization of the pinned ferromagnetic layer or the freeferromagnetic layer is decreased, the increase of the dematnetizationfield or the static magnetic field can be restricted. Thus, the problemconcerning to magnetizing in an MRAM device can be solved.

In the present invention, the diffusion preventing layer is provided inthe magneto-resistance element. Therefore, Mn and Ni diffusion from theMn-based anti-ferromagnetic layer and Ni-based free ferromagnetic layerinto the tunnel insulating layer can be prevented. Further, the problemscan be solved such as the increase of the additional resistance due toaddition of the diffusion preventing layer, and the decrease of themagnetic coupling in the pinned ferromagnetic layer and the freeferromagnetic layer. Thus, compared with the conventional technique, themagnetic tunnel device with higher thermal resistance can bemanufactured at lower cost. The improvement of the thermal resistance ofthe magneto-resistance device contributes to improvement of thereliability and the thermal stability of the magnetic memory deviceusing the magneto-resistance device. Moreover, a manufacturing processmargin extends in the magnetic memory device with the magneto-resistancedevice, and it is possible to manufacture devices with higherperformance.

1. A magneto-resistance device comprising: an anti-ferromagnetic layer;a pinned ferromagnetic layer having a fixed spontaneous magnetizationand coupled with said anti-ferromagnetic layer; a non-magnetic tunnelinsulating layer coupled with said pinned ferromagnetic layer; and afree ferromagnetic layer coupled with said tunnel insulating layer andhaving a reversible free spontaneous magnetization, wherein said pinnedferromagnetic layer comprises a first composite magnetic layerconfigured to prevent at least one of elements of saidanti-ferromagnetic layer from diffusing into said tunnel insulatinglayer.
 2. The magneto-resistance device according to claim 1, whereinsaid anti-ferromagnetic layer contains Mn, and said first compositemagnetic layer prevents said Mn from diffusing into said tunnelinsulating film.
 3. The magneto-resistance device according to claim 1,wherein said first composite magnetic layer comprises: ferromagneticmaterial that has been not oxidized; and oxide of a material which iseasy to combine with oxygen compared with said ferromagnetic material.4. The magneto-resistance device according to claim 3, wherein saidferromagnetic material contains Co in as a main component.
 5. Themagneto-resistance device according to claim 1, wherein said firstcomposite magnetic layer is formed from a region of an amorphous phaseas a whole or from a region of said amorphous phase and a region of acrystalline phase.
 6. The magneto-resistance device according to claim5, wherein said crystalline phase region contains a plurality of crystalregions, and said plurality of crystal regions pass through said firstcomposite magnetic layer into a direction of a thickness of said firstcomposite magnetic layer.
 7. The magneto-resistance device according toclaim 5, wherein a composition of said amorphous phase in said firstcomposite magnetic layer is D_(Z)M_(1-Z)O_(X) (0.6≦Z≦0.9 and X>0), saidD is at least one selected from the group consisting of Co, Fe and Ni,and said M is at least one selected from the group consisting of Ta, Zr,Hf, Nb, and Ce.
 8. The magneto-resistance device according to claim 1,wherein said first composite magnetic layer contains a plurality ofcrystal grains comprising ferromagnetic material, said plurality ofcrystal grains are separated from each other by oxide, and a part ofsaid plurality of crystal grains contacts an adjacent one of saidplurality of crystal grains.
 9. The magneto-resistance device accordingto claim 8, wherein said oxide comprises oxide of at least an elementselected from the group consisting of Al, Si, Mg and Ti.
 10. Themagneto-resistance device according to claim 1, wherein said firstcomposite magnetic layer contains a plurality of crystal grainscomprising ferromagnetic material, and said plurality of crystal grainsare separated from each other by oxide and pass through said firstcomposite magnetic layer into a direction of a thickness of said firstcomposite magnetic layer.
 11. The magneto-resistance device according toclaim 10, wherein a part of said plurality of crystal grains contacts anadjacent one of said plurality of crystal grains.
 12. Themagneto-resistance device according to claim 10, wherein said oxidecomprises oxide of at least an element selected from the groupconsisting of Al, Si, Mg, Ti, Ta, Hf, Zr, Nb and Ce.
 13. Themagneto-resistance device according to claim 8, wherein a thickness ofsaid oxide is thinner than a grain diameter of each of said plurality ofcrystal grains.
 14. The magneto-resistance device according to claim 13,wherein the thickness of said oxide is equal to or less than 2 nm. 15.The magneto-resistance device according to claim 14, wherein an averagegrain diameter of said plurality of crystal grains is equal to or lessthan 10 nm.
 16. The magneto-resistance device according to claim 8,wherein ferromagnetic coupling is kept between said plurality of crystalgrains.
 17. The magneto-resistance device according to claim 1, whereinsaid pinned ferromagnetic layer further comprises a first metalferromagnetic layer and a second metal ferromagnetic layer, and saidfirst composite magnetic layer is interposed between said first metalferromagnetic layer and said second metal ferromagnetic layer.
 18. Themagneto-resistance device according to claim 1, wherein a resistivity ofsaid first composite magnetic layer is in a range of 10 μΩcm to 3000μΩcm.
 19. The magneto-resistance device according to claim 1, whereinsaid free ferromagnetic layer comprises: a second composite magneticlayer configured to prevent at least one elements of said freeferromagnetic layer from diffusing into said tunnel insulating layer.20. The magneto-resistance device according to claim 19, wherein saidfree ferromagnetic layer contains Ni, and said second composite magneticlayer prevents said Ni from diffusing into said tunnel insulating film.21. The magneto-resistance device according to claim 20, wherein saidfree ferromagnetic layer comprises: a metal ferromagnetic layer providedbetween said tunnel insulating layer and said second composite magneticlayer; and a soft magnetic layer containing said Ni said secondcomposite magnetic layer on an opposite side to said metal ferromagneticlayer.
 22. The magneto-resistance device according to claim 1, whereinsaid pinned ferromagnetic layer comprises: a non-magnetic layer; and twoferromagnetic layers anti-ferromagnetically coupled to each otherthrough said non-magnetic layer.
 23. The magneto-resistance deviceaccording to claim 19, wherein said free ferromagnetic layer comprises:a non-magnetic layer; and two ferromagnetic layersanti-ferromagnetically coupled through said non-magnetic layer.
 24. Amagnetic memory comprising a magneto-resistance device which comprises:an anti-ferromagnetic layer; a pinned ferromagnetic layer having a fixedspontaneous magnetization and coupled with said anti-ferromagneticlayer; a non-magnetic tunnel insulating layer coupled with said pinnedferromagnetic layer; and a free ferromagnetic layer coupled with saidtunnel insulating layer and having a reversible free spontaneousmagnetization, wherein said pinned ferromagnetic layer comprises a firstcomposite magnetic layer configured to prevent at least one of elementsof said anti-ferromagnetic layer from diffusing into said tunnelinsulating layer.
 25. (canceled)
 26. (canceled)
 27. (canceled)
 28. Themagnetic memory according to claim 24, wherein said free ferromagneticlayer comprises: a second composite magnetic layer configured to preventat least one elements of said free ferromagnetic layer from diffusinginto said tunnel insulating layer.
 29. A magneto-resistance devicecomprising: an anti-ferromagnetic layer; a pinned ferromagnetic layerhaving a fixed spontaneous magnetization and coupled with saidanti-ferromagnetic layer; an intermediate layer coupled with said pinnedferromagnetic layer; and a free ferromagnetic layer coupled with saidintermediate layer and having a reversible free spontaneousmagnetization, wherein at least one of said pinned ferromagnetic layerand said free ferromagnetic layer comprises a first composite magneticlayer configured to prevent at least one of elements of a correspondingone of said anti-ferromagnetic layer and said free ferromagnetic layerfrom diffusing into said intermediate layer.